The purpose of this study is to determine relationships among the timing and duration of sleep and levels of stress, performance, health status and hormones. Not everyone has the same preferences for morning and evening activities, including when they choose to get up and to go to bed. Apparently such preferences are directly influenced by genetically timed biological mechanisms. Because of these differences, people vary in their individual highest activity level and their least effective performance across different times of day and night. Also, when people are forced to live on schedules very much different than their natural body times, such as for night and shift work, many psychobiological factors can be affected in the long run, including stress reactivity, general health, hormone profiles, performamce and alertness.